Various lamps mounted externally on a motor vehicle convey important information to pedestrians and drivers of other vehicles. In particular, lamps mounted on the sides of a vehicle, referred to as turning signal lamps, indicate which direction the vehicle is about to turn. When the driver is about to turn the vehicle left, for example, he or she activates the left turn signal switch, whereupon the lamp mounted on the left side of the vehicle flashes on and off; correspondingly, when the driver is about to turn the vehicle right, he or she activates the right turn signal switch, whereupon the lamp mounted on the right side of the vehicle flashes on and off.
When not being used to indicate which direction the vehicle is about to turn, the turning signal lamps may also operate as emergency signal lamps to indicate that the driver of the vehicle is in distress, or that the vehicle has been tampered with. In this case, the driver manually activates (or the vehicle's alarm system automatically activates) an emergency signal switch, whereupon both of the lamps flash on and off together.
Still further, the turning signal lamps may operate as vehicle running lights, to indicate the presence of the vehicle. That is, when not operating as turning signal lamps or emergency signal lamps, the lamps may constantly burn when the vehicle is in use, even during daylight hours, to enhance the visibility of the vehicle. This enhanced visibility proves particularly advantageous for smaller vehicles, such as motorcycles, that are often overlooked by other drivers.
Using the same lamps to serve multiple purposes in this way is often preferred over having separate, dedicated lamps for each purpose, but the multi-purpose use complicates the vehicle's lighting control system. Some control systems, for instance, require large arrangements of transistors and other components, which is problematic for the smaller vehicles that have a particular need for enhanced visibility. Other control systems that are well suited for smaller vehicles nonetheless fail to provide desired functionality, e.g., to permit operation of the lamps as emergency signal lamps while the vehicle is off or otherwise not in use.